Vapor cell light amplifier



4 Sheets-Sheet 1 INVENIOR J. W. HORTON VAPOR CELL LIGHT AMPLIFIER May 12, 1964 Original Filed July 22, 1959 las@ ATTORNEYS Jolla/ZUM BY nu; f

May 12, 1964 J. w. HoRToN 3,133,199

vAPoRcELL LIGHT AMPLIFIER Original Filed July 22, 1959 4 Sheets-SheetI 2 IDPQ VAL//f/ Muff 2 INV ENTOR Jolwllolfm ATTORNEYS 4 Sheets-Sheet 3 J. W. HORTON VAPOR CELL LIGHT AMPLIFIER May 12, 1964 original Filed July 22, 1959 4 Sheets-Sheet 4 'May 12, 1964 J. w. HoRToN VAPOR CELL LIGHT AMPLIFIER original Filed July 22,'1959 im .ml/,f gwn Ma/ 05M PMP M u.. m m n 4 P l. M n. I w w J s i@ M M W M w M I IIMIN@ l if AVI! lli nlm A NNW u, y Hhlllvwlhwvllhuhlwl United States Patent O 3,133,199 VAPOR CELL LIGHT AMPLIFIER John W. Horton, New York, N.Y., assignor to International Business Machines Corporation, New York, N.Y., a corporation of New York Original application July 22, 1959, Ser. No. 828,908, now Patent No. 3,098,112, dated July 16, 1963. Divided and this application Oct. 9, 1962, Ser. No. 234,273 7 Claims. (Cl. Z50- 213) This invention relates to an optical device that provides light :amplilication and find-s additional util-ity las a logi-cal device. The invention also relates to systems employing said device.

This application is a division of application Serial No. 828,908, tiled July 22, =1959, now U.S. Patent No. 3,098,- 112, granted July 16, 1963.

In the prior art, light amplification has usually been accomplished by conversion of light energy into electrical energy, ampliiication of the electrical energy and reconversion of the ampliiied electrical energy to light energy. The present invention however, eliminates the intermediate couver-sion -to electrical energy, and performs the ampliication more directly via the action of one light beam upon the properties of a material medium which controls the transmission of a second light beam. The means by 'which this is accomplished involves illumination of a vaporou-s medium with beams of electromagnetic .radiations. A correlated functioning of such a device is that of a logical element. In the continuing presence of a single beam, identified as the pumping radiation, the medium is rendered excessively translucent to the pumping radiation but in the presence of two beams, namely, a .pumping radiation and a de-pumping radiation, the medium is restored to a more nearly normal condition of the vapor which is relatively opaque to the pumping rediation. It can be seen then that the vapor is either opaque or translucent las .a function of the presence or absence of the depumping radiation. This provides its function las a lom'cal device. Additionally, in accordance this invention, small modulations oi? the de-pumping radiation provide large modulations of the pumping radiation to exhibit the light amplifying qualities of this invention.

It is, therefore, one object of this invention to provide an optical device which exhibits light amplification.

It is also an object of this invention to provide an optica-l device which has particular 4utility as `a logical element. A

Further objects of the invention include the use of this device in systems including light ,amplilication and/or optical logic.

These and other objects will become apparent from a detailed description and the accompanying drawings.

In the drawings:

FIG. 1 is a chart plotting A energy as ergs against magnetic field in gauss showing Zeeman splitting of the two hyperne states `for the ground and excited states of sodium vapor;

FIG. 2 is Ia diagrammatic representation of one form of light cell constructed in accordance with this invention;

FIG. 3 is a diagrammatic representation of two light cells constructed in accordance with this invention and coupled to form a photon-valve amplier.

PIG. 4 is a diagrammatic representation of the coupling of two light cells constructed in accordance with this invent-ion functioning :as a flip-dop;

FIG. 5 is a diagrammatic representation of a means of directprocessing of light information constructed vin accordance with this invention;

lFIG. 6 is a diagrammatic representation of an optical system employing a light cellconstructed in accordance 3,133,199: Patented May l2, 1964 with invention in which the pumping and depumping radiations enter said cell in parallel.

FIG. 7 is a diagrammatic representation of one means of converting electronic data into light data by modulation of the Ide-pumping radiation; and

1FIG. 8 is a diagrammatic representation of another form of light cell constructed in accordance with this invention.

lReferring first to FIG. 1, there is shown a plot of energy in ergs versus static magnetic field in gauss, for sodium atoms in a vapor state. At magnetic ground (0 gauss) the sodium atoms are in the ground state (S1/2) and are divided between two hyperline states, F=2 and F=l. F is a measure of the total angular momentum vector of the latom which is expressed by the classical formula:

Where I is the vector representing the spin angular momentum of the sodium nucleus and J is the vector representingrthe total angular momentum of the planetary electrons. In quantum mechanics, the relation between F, I, and l is that F=(I-{]), (l-I-J-l), (I-J). When F, I, and I are now quantum numbers which rare measures of the respective angular momento. just mentioned. The value or I in this particular case is 3/ 2 and that of I is 1/2, giving the two hyperine states where F22 and F=1. In the S1 /2 ground state, the total orbital angular momentum (L) of Vall the sodium electrons is zero, that is, the electrons oscillate to and iro requiring la passage thereof through the nucleus. Since all the electrons in sodium are paired oit in electron spin except for a single outermost valence electron, the total angular momentum of electrons of the sodium atom J is according to the quantum mechanical rule J: (L-l-S), (L-lS-l) (L-2)=('0}1/2)=1/2 In the ground state there are live atoms out of every eight in F=2 hype-rime state and the three remaining atoms in the F =1 hyperne state. By the application to the vapor of relatively weak static magnetic lfield, in the order of about ten gauss, Zeeman splitting of the hyperfine states takes place. The F :2 hyper-line state atoms oriented one each into tive magnetic sublevels, identified as MF={-2, -l-l, 0, -1 and 2, and the F=1 hypertine state atoms yare oriented one each into the three magnetic sub-levels MF=l-l, O, -1 where MF is the magnetic quantum number. beam of pumping radiation such that sub-level transitions of the .atoms take place in accordance with the absorption selection rule AMF=|1, said transitions taking place between the ground state and the excited state (P1/2) by absorption of a photon from this radiation by the atom, the excited atom `will jump to a subalevel in the excited state governed by this selection rule. In the case ot sodium vapor such a resonance pumping radiation is the D1 sodium line, right circularly polarized relative to the magnetic iield and directed parallel to it. Its frequency is 5.09 108 megacycles and when multiplied `by Plancks constant (6.6X10-27) provides the necessary Under the influence of the resonance pumping radia-A tion, an atom will jump, for instance, from the MF=0 subelevel in the ground state to the MF=+1 sub-level in the excited state. This is in accordance with the previously cited selection rule for adsorption. However, the selec-` Ilf now the vapor is subjected to a This selection rule is Therefore, upon emitting its energy in the excited state, the'atom which had been jumped from the ground state to the excited state and into sub-level MF=+1 can return to one of three sub-levels in the ground state, namely MF={-l, MF=0, or MF=+2- All of the sub-levels in the ground state, with the exception of the sub-level MF=i-2 are absorbing to the resonance pumping radiation. This latter sub-level is non-absorbing to the pumping radiation. There is no excited state sub-level to which an atom may jump from the SM2; MF: |2 level, sinceV there is no P1 /2 state sub-level MB1-+3, which of course there would have to be in order to satisfy the absorption selection rule. Therefore, the sub-level in the ground state MF=+2 traps all atoms which by their transitions between the ground and the excited state and back again, land therein. On the average seven photons from the pumping radiation are required to position a sodium atom in this non-absorbing sub-level of the ground state. Eventually then, substantially all of the atoms populate this non-absorbing sub-level in the ground state. This is the only non-absorbing sub-level to the pumping radiation in the ground state, all of the other sub-levels being absorbing thereto. Therefore, under the conditions where each of the sub-levels in the ground state are substantially equally populated, the pumping radiation is substantially diminished in intensity due to the relative opacity of the medium to it because of the absorption from the radiation of its photons by the atoms in the absorbing sub-levels. Ultimately, however, upon substantially 100% orientation of the atoms in the non-absorbing sub-level (MF=}2) the incident intensity of the pumping radiation is substantially regained at the exit end of the cell. The vapor then becomes substantially translucent-and excessively so-to the pumping radiation.

Now, if there is applied to the medium a second beam of electromagnetic energy, identified as the depumping radiation, which second beam causes transitions in accordance with the selection rule differing Arom AMF=+ l, then the non-absorbing orientation will be destroyed. The nonabsorbing sub-level will become substantially depopulated and then the medium again becomes relatively opaque to the transmission therethrough of the pumping radiation. It must be noted that whereas before it required the absorption of seven photons per atom to cause transitions into the non-absorbing sub-level, the transition from the non-absorbing to an absorbing sub-level required only a single photon per atom. Consequently, it can be seen that by a relatively small modulation of the de-pumping radiation, a relatively high modulation of the pumping radiation is obtained. Therefore, this particular device exhibits true light amplification, AIt may be noted that the presence of the de-pumping radiation causes a large diminution of the pump radiation. This is amplification with a 180 phase reversal, analogous to that produced by the triode vacuum tube.

Turning to FIGURE 2, there is shown a schematic of a device constructed in accordance with this invention. The pumping radiation 10 obtained from a suitable source is a right circularly polarized D1 line of sodium propagated in a'direction parallel to the magnetic field Ho. The depumping radiation enters the vapor cell 11 at right angles thereto, the de-pumping radiation being identified by the numeral 12. The vapor within the cell is sodium vapor in argonbuffer gas at 500 K. and at a pressure of 2 l0-5 mm. Hg. Under the conditions outlined above, provided the intensity of the pumping radiation equals the intensity of the de-pumping radiation, the ratio of intensity of the pumping radiation entering the cell (IP) IN compared to that of the pumping radiation leaving the cell (IP) OUT is approximately l to 1. The photon gain, when the depumping radiation intensity is about 1/2 of that of the pumping radiation, is between l, 3 and 2.

So it can be seen that the device functions as a logical element having two states, namely, an opaque and a translucent state, depending upon the presence of one or two of the radiations, and also exhibits photon gain.

Referring to FIGURE 3, there is shown a photon-valve amplifier chain showing the compatability of a plurality of these units, which is very much the same as the compatability of vacuum tubes which are arranged in cascade. If we connect two of the cells, as shown in FIGURE 2 in cascade as shown in FIGURE 3, it can be seen that the photon gain achieved by the pumping radiation IPI within the cell 13 can be applied as the de-pumping radiation IDPZ in cell 14. A small modulation of the de-pumping radiation IDPI will provide a relatively greater modulation of the pumping radiation pl. This larger modulation applied to cell 1li as the de-pumpingradiation 1m32 will produce a still further increase in modulation of the pumping radiation 1PZ. The output would then be characteristie of the amplification factors of the two cells 13 and 14. The means by which the radiations are coupled between cells is by an conventional optical means which will preserve the polarization of the coupled beams.

Referring to FIGURE 4, there is shown a photon-valve iiip-op which is comparable to a vacuum tube hip-op and functions as a storage cell having an on and off or binary l-binary 0 condition. As shown in this figure, upon the application to the respective vcells of pumping radiation 1p1 and pumping radiation 1PZ, cell 16 is in the off condition and cell 15 is in the on condition. The output from cell 15, I1, is fed to cell 16 as the de-pumping radiation to make this cell substantially opaque to the pumping radiation.v Consequently, I2 at the outputof cell i6 is equal to substantially zero, and provides no de-pumping radiation to cell 15. Consequently, cell 15 is substantially translucent to the pumping radiation IPI. However, should, for instance, momentarily 1p1 be shut off, while 1PZ remains on, the opposite conditions would prevail. In this caseI1 would be equal to zero, providing no de-pumping input to cell 16. Therefore, the pumping radiation lpg in cell 16 would provide an output I2 equal to some value. Therefore, cell 16 would be on and cell 15 would be olf.

Turning now to FIGURE 5, there is shown a system for the direct processing of light information. The light sources for the pumping radiation (P) and for the depumping radiation (DP), are indicated by the Xs. The various cells are indicated att-17 to 2'7, inclusive. The data tape is identified by numeral 27. It has a plurality of data punches indicated at 29, 30 and 31. The control tape 32 has a plurality of punches thereinv indicated at 33 and 34. For example, there is shown the routing of information indicated by punch-hole 29 to position 35 on the film 36. Cell 17 because of a lack of coincidence of radiations is translucent. The output from cell 17 is fed to cells 18 and 22. Because of the coincidence of radiations in cell 1S, this cell is opaque to the pumping radiation and provides no output to cells 19 and 20. However, because of the lack of coincidence of radiations in cell 22, the pumping radiation provides an output therefrom which is fed to cells 21V and 23. In this particular case, because of the control tape punchhole at 34, cell 23 has a coincidence of radiations therein and is opaque to the pumping radiation, while cell 21 has a lack of coincidence of radiations therein and is translucent. Therefore, the output of the pumping radiation from cell 21 is recorded at position 35 on the film 36. By moving the control tape in conjunction with the data tape, the data can be switched to any particular position on the film 26 as determined by the control tape. While we have here shown a particular shape of punch, that is, a circle, on the data tape and control tape, other shapes may be employed. For instance, these holes may be replaced by negative containing images thereon, thus shaping for instance the pumping radiation. In this event, it is quite clear how this image of the negative can be transferred under the control of the control tape to a particular point or points on the film strip 36. Additionally, the control tape may have a particularly shaped aperture, created by a negative to superimpose the image of the control tape onto the image of the data tape to provide a composite output of the lm 36. Y

As can be seen if the control tape had a hole only at position 34, then the image of 29 could be switched through cells 19 and 20 in addition to cell 21. So it is possible with this arrangement to not only pick one particular place on the output to store the data but a plurality of selected positions may be obtained. As referred to above, in the case of negatives having images thereon in place of the holes these negatives may carry, for instance, alpha or numeric characters. The control tape might carry the image of a business form.

What has thus far been illustrated is the use of a sodium vapor as the vapor within the light cell, but the invention is not so limited. Other vapors may be substituted. These include all of the alkali vapors and gases such as helium and hydrogen. Other such media are known in the art. Generally speaking, the vapor or gas should have the following characteristics:

(1) A ground state (includes metastable state of a gas).

(2) An excited state.

(3) The vapor or gas must exhibit splitting into a plurality of Zeeman levels upon the application thereto of a magnetic field.

(4) One of the levels must be a photon non-absorbing level to the pumping radiation, or there must be at least one level which can be preferentially occupied and which has an average absorption less than the average of all the ground state levels. i

Additionally, we have illustrated as the pumping radiation only the D1 sodium line. However, other sources may be used. Such sources are known in the art. The radiation must for all practical purposes be a resonant radiation, that is, in resonance With the vapor employed, and must cause Zeeman transitions between the magnetic sub-levels and these transitions may take place in accordance with the absorption selection rule AMF=11 as in the case of right circularly polarized radiation, or AMF=1 as in the case of left circularly polarized radiation. In other words, the pumping radiation must be a resonance radiation and must pump the atoms of the vapor into a lZeeman level which is non-absorbing to it.

The de-pumping radiation should be a radiation which does not obey the same selection rule as the pumping radiation, so that the level which is non-absorbing to the pumping radiation is absorbing to the de-pumping radiation, or if it does obey the same selection rule, then its frequency must be different. For example a right circularly polarized D2 line would obey MF=1 and would de-pump because it jumps the atom into a magnetic sublevel in which MF: +3 occurs. ing action, the de-pump should be resonant, although it need not be.

One particular example has been given in FIGURE 2. This involves the use of a pumping radiation of the D1 line of sodium and a de-pumping'radiation of the same character. The pumping radiation was propagated through the cell at right angles to the de-pumping radiation. This angular diiference was suflicient to provide that the absorption selection rule for the pumping radiation was different from that of the de-pumping radiation, that of the pumping radiation being AMF=+1 since it was a right circularly polarized beam with a direction of propagation parallel to the magnetic eld applied. As long as there is this angular dilference in direction of propagation with this relation observed between field direction and direction of propagation of pumping radiation, the cell will function properly. However, if we assume For maximum de-pump-v 6 two radiations of different characteristics the angular relationship need not be observed. Reference for such a species is made to FIG. 6.

Referring to FIG. 6, the microwave horn 40, which may be a so-called Raytheon rnicrotherm unit, excites a rubidium quartz lamp 41 to provide a rubidium spectrum beam. This beam is divided into two parts 42 and 43 by a reflector 44. Beam 42 is directed by lens system 45 through the circular polarizing sheet 46. Let it be assumed that this beam is right circularly polarized thereby. It then passes through the beam splitter 47 to the interference lter 48. This filter 48 prevents all but the resonance radiation line of the spectrum from entering through window 49 of cell 50. The cell contains rubidium vapor.

The beam 43 passes through lens system 51 to reector 52 and thence through the chopper assembly including lenses 53 and 54 and mechanical chopper 55 where said beam is modulated. The modulated beam is reilected by reflector 56 through left circular polarizing sheet 57 to the beam splitter 47 and thence through filter 4S and window 49 into the cell 50.

The output of the cell Si) from the exit window 62 is directed by lens 58 and reflector 59 to the photomultiplier 60. The photomultiplier detects the output of the vapor cell 50 and indicates the modulations induced by the chopper.

Here then is an example of parallel entry of both beams. A weak static magnetic lield, not shown, is applied to the cell with the field direction parallel to the direction of propagation of the beams. The beam 42 may be considered to be the pumping radiation and beam 43 the de-pumping radiation. The former may be right circularly polarized or left circularly polarized depending upon the direction of the magnetic field and the latter iS oppositely polarized thereto.

Referring to FIG. 7, there is shown a substitute for the chopper. In this particular case, after beam 43 has been properly polarized by a polarized sheet (not shown) it may enter another vapor cell 61. Again a weak static magnetic eld is applied thereto having a field direction parallel to the direction of propagation of the beam 43. A coil 62 is provided to which is fed the electronic data used to modulate the radiation 43 in the cell 61. This is accomplished by the action of the magnetic eld in the following manner: Let us assume that with a magnetic field (H) pointing to the right in FIGURE 7 and with the incident light right circularly polarized, the vapor is pumped into the non-absorbing level F :2, MF=2 and is thereby rendered excessively translucent. When the magnetic field is reversed, the magnetic quantum number is now M F: -2 because the angular momentum vector of the atom has been turned the other Way; now absorption can occur according to the selection rule AMF=+1 more simply, pumping occurs relative to a given direction of the magnetic field; reverse the iield and pumping radiation becomes de-pumping radiation. The output of the cell 61 is fed to the vapor cell 50 as the de-pumpingv radiation; Here We have, of course, assumed that the beam 43 prior to entrance to the cell 61 has been properly polarized and ltered so that it is in resonance with the vapor within the cell 61. FIG. 7 is then an example ofv direct conversion of electronic data into optical data kfor employment in the system of the present invention.

Another example of parallel entry of pump and depump is shown in FIGURE 8. The generally cylindrical elongated cell 65 may be imagined to be divided into a number of channels which function as individual light cells extending axially of the cell. `Let it be assumed that each channel is l mm. X l mm. Then in Vl square inch We have 25 25=625 channels. Each channel, actually the vapor contained in a channel, may be regarded as a relay in the following sense: Let pump A be turned on through channel A. At first nothing comes out of the cell (relay open), then the pumping action sets in and the vapor becomes excessively translucent (relay closed and stays closed by presence of input signal). Next, support we pass de-pump A through channel A; this cuts off output (relay is opened by de-purnp). A plurality of photomultipliers as shown in FIGURE 6 may be positioned at the output end of each channel to determine the condition of the relays. So we have here 625 relays. These relays can operate at speeds around l to 2 kc.

When an atom has been trapped in the non-absorbing level its movement in the cell may cause it to collide with the walls thereof. By virtue of this collision it may lose its spin and become absorbing to the pumping radiation. This has two deleterious effects; (a) for given pumping light intensity the vapor is less translucent and (b) to achieve a desired degree of translucency (say 90%) the pumping radiation would have to be increased to compensate for the de-pumping effect of the wall. To decrease this probability and to thereby increase the relaxation time of the atoms, two supplemental techniques may be employed. First, a buffer gas of neutral characteristics may be employed. The rare gases such as argon, neon, etc. are examples. Secondly, the walls may be coated with a saturated long chain hydrocarbon having all of its electrons paired off. Such an example is polyethylene. By employing these techniques the lifetime of an atom in the non-absorbing level is substantially increased, perhaps by a factor of l()G as compared to a cell having no such coating or containing no buffer gas. Preferably the cell walls are translucent to allow escape of random light. The` Windows are ground and stress annealed so that they provide no depolarizing effect on the radiations.

What has been shown and described are specific embodiments of the present invention. Other embodiments obvious to those skilled in the art from the teachings herein are contemplated to be within the spirit and scope of the following claims.

What is claimed is:

l. An optical two-state device comprising two light cells each having a light medium therein adapted to split into a plurality of Zeeman magnetic sub-levels, a magnetic eld for application to the media of each of said cells to cause said splitting, a pumping radiation associated with each of said cells for illuminating said medium therein and for pumping the atoms of said medium into a Zeeman sub-level relatively non-absorbing thereto whereby said sub-level becomes highly populated, means to cross couple the output pumping radiation from each of said cells to function as the input de-pumping radiation to each of said cells, said depumping radiation depopulating said non-absorbing sub-level and means to control at least one of said input pumping radiations.

2. An optical two-state device comprising two light cells each having a light medium therein adapted to split into a plurality of energy levels, a source of pumping radiation associated with each of said cells for illuminating said medium therein and for pumping the atoms of said medium into an energy level relatively non-absorbing thereto whereby said energy level becomes highly populated, means to cross-couple the output pumping radiation from each of said cells to function as the input depumping radiation to each of said cells, said de-pumping radiation de-populating said non-absorbing energy level and means to control at least one of said input pumping radiations.

3. The optical two-state device recited in claim 2 wherein said medium is one selected from the group comprising helium, hydrogen and the alkali vapors.

4. An optical two-state device comprising two light cells each having a light medium therein adapted to split into a plurality of Zeeman magnetic sub-levels, means for applying a magnetic field to the medium of each of said cells to cause said splitting, a source of pumping radiation associated with'each of said cells for illuminating said medium therein and for pumping the atoms of said medium into a Zeeman sub-level relatively non-absorbing thereto whereby said sub-level becomes highly populated, means to cross-couple the output pumping radiation from each of said cells to function as the input de-pumping radiation to the other of said cells, said de-purnping radiation de-populating said non-absorbing sub-level and means to control at least one of said input pumping radiations.

5. The two-state optical device recited in claim 4 wherein the direction of said magnetic field is the same as the direction of propagation of said pumping radiation.

6. An optical two-state device comprising two light cells each having a light medium therein, said medium having the following characteristics:

(l) a ground state,

(2) an excited state,

(3) exhibits splitting into a plurality of Zeeman levels upon the application to said medium of a Weak static magnetic field,

(4) one of said levels is a photon relatively non-absorbing level to a pumping radiation, means providing a weak static magnetic lield for application to said medium to cause said splitting, a source of a beam of pumping radiation for illuminating said first light cell, a source of a beam of pumping radiation` for illuminating said second cell, both of said sources of pumping radiation causing Zeeman transition of substantially all of the atoms of said medium to said non-absorbing level whereby said non-absorbing level becomes highly populated and said medium becomes translucent to said pumping radiation, means to cross-couple the output pumping radiation from each of said cells to function as the input de-pumping radiation to each of said cells, said sources of depumping radiation being effective to illuminate the medium of each of said cells to cause said non-absorbing level to become de-populated and said medium to become substantially opaque to said pumping radiation, means to control said radiations, the direction of said magnetic field being the same as the direction of propagation of said pumping radiation, said de-pumping radiations being of substantially identical frequency and direction of polarization, said de-pumping radiation being propagated in the direction at right angles to said field direction.

7. An optical two-state device comprising two light cells each having a light medium therein adapted to split into a plurality of energy levels, a source of pumping radiation associated With the rst of said cells for illuminating said medium therein and for pumping the atoms of said medium into an energy level relatively non-absorbing thereto whereby said energy level becomes highly populated, said first light cell providing a light output when said non-absorbing energy level is highly populated, means connecting the light output of said first cell to said second cell to provide a source of pumping radiation thereto, the light output of said first cell pumping the atoms of the light medium in said second cell into an energy level relatively non-absorbing thereto whereby said energy level becomes highly populated, and means for supplying de-pumping radiation to said second cell to depopulate said non-absorbing energy level.

No references cited. 

1. AN OPTICAL TWO-STATE DEVICE COMPRISING TWO LIGHT CELLS EACH HAVING A LIGHT MEDIUM THEREIN ADAPTED TO SPLIT INTO A PLURALITY OF ZEEMAN MAGNETIC SUB-LEVELS, A MAGNETIC FIELD FOR APPLICATION TO THE MEDIA OF EACH OF SAID CELLS TO CAUSE SAID SPLITTING, A PUMPING RADIATION ASSOCIATED WITH EACH OF SAID CELLS FOR ILLUMINATING SAID MEDIUM THEREIN AND FOR PUMPING THE ATOMS OF SAID MEDIUM INTO A ZEEMAN SUB-LEVEL RELATIVELY NON-ABSORBING THERETO WHEREBY SAID SUB-LEVEL BECOMES HIGHLY POPULATED, MEANS TO CROSS COUPLE THE OUTPUT PUMPING RADIATION FROM EACH OF SAID CELLS TO FUNCTION AS THE INPUT DE-PUMPING RADIATION TO EACH OF SAID CELLS, SAID DEPUMPING RADIATION DEPOPULATING 